Ultrasonic transducers are used in many medical applications and, in particular, for the non-invasive acquisition of images of organs and conditions within a patient, typical examples being the ultrasound imaging of fetuses and the heart. The ultrasonic transducers used in such applications are generally hand held, and must meet stringent dimensional constraints in order to acquire the desired images. For example, it is frequently necessary that the transducer be able to obtain high resolution images of significant portions of a patient's chest cavity through the gap between two ribs when used for cardiac diagnostic purposes, thereby severely limiting the physical dimensions of the transducer. As a consequence, and because of the relatively small aperture between human ribs and similar constraints upon transducer positioning when attempting to gain images of other parts of the human body, there has been significant development of linear or phased array transducers comprising multiple transmitting and receiving elements, with the associated electronics and switching circuits, to provide relatively narrowly focused and "steerable" transmitting and receiving "beams".
Many such transducers are comprised of a one element wide by multiple element long linear array of transmitting and receiving elements arranged in line along a flat plane or, preferably, along a concave or convex arc, thereby providing a greater scanning arc. The transmitting and receiving beams of such transducers are formed and steered by selecting individual transducers elements or groups of transducer elements to transmit or receive ultrasonic energy, wherein each such individual transducer element or group of transducers elements forms an "aperture" of the transducer array. Such an array is thereby formed of a single row of apertures extending along the face of the array and such transducers are consequently referred to as "single aperture" transducers.
There also transducers that are capable of scanning or focusing in elevation as well as azimuth, that is, along the axis at right angles to the azimuth plane along which the elements are arrayed as well as along the azimuth plane. As is well understood, the formation, steering and focusing of the transmitting and receiving beams of a transducer are controlled by selection and use of the various separate physical divisions or areas of transducer material comprising the transducer array, which, as described above, are referred to as "apertures". In contrast to "single aperture" transducers, however, in which each aperture is formed by an element or group of elements extending across the face of the array as a single unitary area or division or the array, each corresponding element in a transducer capable of scanning in elevation is divided into multiple sub-elements, or segments. For this reason, and because each element position along such an array can form multiple apertures, that is, using different combinations of the sub-elements or segments of each of the transducer elements, such transducers are consequently referred to as "multiple aperture" transducers. The shape, focus and direction of the transmitting and receiving beams of a multiple aperture transducer are again controlled by selection of the apertures of the array. In a multiple aperture array, however, each aperture is formed by one or more of the sub-elements, or segments, of the transducer elements, so that the apertures of a multiple aperture array can be used to steer and focus the transducer scan beam along the elevation axis as well as along the azimuth axis and can define multiple azimuthal scan planes, each being at a different angle of elevation.
Single and multiple aperture transducers are generally constructed from a single piece of transducer material having a width equal to the length of one element and a length equal to the widths of the total number of elements, plus spaces between the elements. One or more element interconnection circuits providing conductive connections and paths interconnecting the individual elements or segments and forming the apertures of the transducer are bonded to one side of the piece of transducer material and a layer or layers of matching material may be bonded to the radiating and receiving side of the transducer material. The assembly comprised of the transducer material, element interconnection circuits and matching layers, if any, is referred to as a "stack" and a temporary or permanent layer of backing material of some form, such as a flexible material, may be bonded to the back of the stack, for example, to aid in handling the stack during manufacture or to comprise a part of the structure of the finished transducer assembly. In addition, one or more layers of impedance matching material is often superimposed upon the transducer elements to match the acoustic impedance of the transducer to the body or material being scanned, and a lens comprised of a suitable material may be additionally superimposed upon the impedance matching material to shape or focus the beams generated by the transducer elements. In some implementations, the impedance matching layers may have suitable acoustic characteristics and may be shaped to operate as an acoustic lens.
A transducer is used in conjunction with a set of transducer electronics that typically include transmitting electronics for driving the aperture elements and segments to generate the ultrasonic signals transmitted by the transducer, receiving electronics for receiving the signals representing the returned ultrasonic signals, and switching elements for selectively connecting the transmitting and receiving electronics to the elements and segments of the apertures to select the aperture or apertures for each transmitted or received signal. It is therefore necessary to provide electrical connections between the apertures, that is, the element interconnection circuits interconnecting the elements and segments of the transducer array to form the apertures, and the transducer electronics and these connections are typically provided through flexible printed circuits and wires running along the body of the transducer.
Providing the electrical connections between the transducer electronics and the elements, sub-elements and segments of the arrays remains a primary problem in constructing transducers, however, particularly as the number of apertures increases. That is, the physical dimensions of an array, especially for medical use, is generally constrained, for example, by the need to scan the cardiac structures through the space between patient's ribs to avoid interference by the ribs. A typical transducer, however, will contain 96 to 128 or more elements or segments which may be used individually or in combinations as apertures, each of which must be individually connected to the transducer electronics.
In a typical transducer, the element interconnection circuits may be comprised, for example, of flexible printed circuits while the connections to the elements and segments are typically brought out for connection to the transducer electronics through a flexible printed circuit. The flexible printed circuit has a lead for each aperture of the transducer and each flexible printed circuit lead is, in turn, connected to a wire of a cable connected to the transducer electronics. In other designs, the wires of the cable connected to the transducer electronics may be connected directly to the element interconnection circuits.
The flexible printed circuit leads and cable wires connecting the apertures connected to the transducer electronics are typically laid out in a transverse orientation relative to the element array, that is, in a straight line from the transducer, so that each flexible printed circuit lead and corresponding cable wire lie in a straight line, thereby requiring a space per wire of at least the diameter of the wire. The flexible printed circuit, the connections between the flexible printed circuit and the cable, and the transducer end of the cable are typically contained within the transducer case, that is, in the "handle" section of the transducer behind the transducer head, and, in a typical 96 to 128 element transducer, thereby require substantial width in the transducer case. This, in turn, results in a relatively bulky and hard to handle transducer.
While it is possible to reduce the size of the transducer "handle", this has typically been accomplished only at the cost of reducing the width of the flexible printed circuit leads and the thickness of the cable wires. This approach, however, results in a mechanically more fragile assembly that is harder to manufacture and more prone to breakage in normal use and that may degrade the quality of the signals between the transducer and the transducer electronics.
In addition, the wires of the cable are typically soldered directly to the flexible printed circuit or, in alternate designs, are run up to the stack and soldered or welded directly to the element interconnection circuits. This requires that the cable wires not only be soldered to the flexible printed circuit during manufacture, but also unsoldered from and resoldered to the flexible printed circuit for repairs to the cable or transducer. Because of the relatively high temperatures involved in soldering and desoldering operations, and in welding operations, there is a significant risk to damage to the flexible printed circuit as well as to the relative fine wires of the cable each time the connections are soldered or unsoldered. As a result, the flexible printed circuit and cable wires can be detached and reconnected only a few times before the cable assembly must be rebuilt or replaced, or the flexible printed circuit is degraded to the point it must be replaced. Also, the transducer stack itself may be damaged in those designs wherein the wires are soldered directly to element interconnection circuits of the stack, so that the transducer stack may have to be replaced.
Finally, it will be noted that the above problems become more difficult with each new generation of transducer designs as there is a need and trend to increase the number of elements or sub-elements to achieve ever finer scan resolution to achieve increasingly detailed images of the anatomic structures, and a correspondingly greater number of connections to be provided.
The present invention provides a solution to these and other problems of the prior art.